The invention relates to a three-phase AC power controller comprising three strands, each having an input and an output with five pairs of valves connected in antiparallel for rotating field reversal, wherein the first input is connected to the first output by way of a first pair, the second input is connected to the second output by way of a second pair and to the third output by way of a third pair and the third input is connected to the second output by way of a fourth pair and to the third output by way of the fifth pair.
Three-phase AC power controllers are categorized as line-commutated converters At a constant frequency the voltage is variably adjusted For this purpose a pair of valves connected in antiparallel, especially thyristors, is arranged in each strand.
Three-phase AC power controllers with rotating field reversal generally comprise five pairs of antiparallel connected valves, as shown in FIG. 1. In such cases one pair is arranged in one strand and in the remaining two strands an input is connected in each case by way of one pair to each output of these two remaining strands. The first pair in the one strand is always activated, in the two remaining strands the activation of the valve pairs is in accordance with the desired direction of rotation of the rotating field. Either the second input is connected via the second pair to the second output and the third input via the fifth pair to the third output or the second input is connected via the third pair and the third input via the fourth pair to the second output.
To relieve the load on the individual strands, in accordance with the prior art, as shown in FIG. 2, an RC branch is arranged in parallel to each pair of valves consisting of a resistor and a series-connected capacitor. In such cases only three branches are ever under load at the same time. For a snubber circuit (another widely used expression is “load-relief circuit” or TSE circuit) of a three-phase AC power controller with rotating field reversal five resistors and five capacitors are thus required, with it being necessary to ensure that the heat arising in the resistors is adequately removed. This leads, especially for three-phase AC power controllers with a power greater than 40 kW, to a corresponding space requirement within the device structure.
The underlying object of the invention is to specify improvements compared to the prior art for a three-phase AC power controller of the type specified at the start.